This work was supported by a Food from Thought Commercialization Grant, which is funded from the Canada First Research Excellence Fund. Canadian Wollastonite provided industrial financial support as part of this Grant.

1. Soil sampling method and core collection
<ol>
	<li>Divide the mapped and a demarcated agricultural land area of interest into different plots based on the land elevation, historical crop yield, and/or land management strategy. Determine the leveling of each plot using a GPS receiver, classify crop yield based on historical farm records (below-average, average, above-average), and the land management strategy used for each plot (types of soil amendments used, if any). Place the flags at the boundaries of each plot to...

<ol>
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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Total+carbon+and+nitrogen+in+the+soils+of+the+world.">Total carbon and nitrogen in the soils of the world.</a> European Journal of Soil Science. 47 (2), 151-163 (1996).</li><li>Haque, F., Chiang, Y. W., Santos, R. 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T., Reynolds, R., Meyers, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facts+about+serpentine+rock+and+soil+containing+asbestos+in+California.">Facts about serpentine rock and soil containing asbestos in California.</a> ANR Publication: University of California. , 8399 (2009).</li><li>Kelland, M. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+yield+and+CO2+sequestration+potential+with+the+C4+cereal+Sorghum+bicolor+cultivated+in+basaltic+rock+dust-amended+agricultural+soil.">Increased yield and CO2 sequestration potential with the C4 cereal Sorghum bicolor cultivated in basaltic rock dust-amended agricultural soil.</a> Global Change Biology. 26 (6), 3658-3676 (2020).</li><li>Haque, F., Santos, R. M., Chiang, Y. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimizing+inorganic+carbon+sequestration+and+crop+yield+with+wollastonite+soil+amendment+in+a+microplot+study.">Optimizing inorganic carbon sequestration and crop yield with wollastonite soil amendment in a microplot study.</a> Frontiers in Plant Science. 11, 1012 (2020).</li><li>Palandri, J. L., Kharaka, Y. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+compilation+of+rate+parameters+of+water-mineral+interaction+kinetics+for+application+to+geochemical+modeling.">A compilation of rate parameters of water-mineral interaction kinetics for application to geochemical modeling.</a> National Energy Technology Laboratory-United States Department of Energy. , (2004).</li><li>Schott, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation,+growth+and+transformation+of+leached+layers+during+silicate+minerals+dissolution:+The+example+of+wollastonite.">Formation, growth and transformation of leached layers during silicate minerals dissolution: The example of wollastonite.</a> Geochimica et Cosmochimica Acta. 98, 259-281 (2012).</li><li>Brioche, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mineral+commodity+summaries-Wollastonite.">Mineral commodity summaries-Wollastonite.</a> US Geological Survey. , (2018).</li><li>Haque, F., Santos, R. M., Dutta, A., Thimmanagari, M., Chiang, Y. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Co-benefits+of+wollastonite+weathering+in+agriculture:+CO2+sequestration+and+promoted+plant+growth.">Co-benefits of wollastonite weathering in agriculture: CO2 sequestration and promoted plant growth.</a> ACS Omega. 4 (1), 1425-1433 (2019).</li><li>Li, Y., Both, A. -. J., Wyenandt, C. A., Durner, E. F., Heckman, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Applying+Wollastonite+to+Soil+to+Adjust+pH+and+Suppress+Powdery+Mildew+on+Pumpkin.">Applying Wollastonite to Soil to Adjust pH and Suppress Powdery Mildew on Pumpkin.</a> HortTechnology. 29 (6), 811-820 (2019).</li><li>Mao, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphate+addition+diminishes+the+efficacy+of+wollastonite+in+decreasing+Cd+uptake+by+rice+(Oryza+sativa+L.)+in+paddy+soil.">Phosphate addition diminishes the efficacy of wollastonite in decreasing Cd uptake by rice (Oryza sativa L.) in paddy soil.</a> Science of the Total Environment. 687, 441-450 (2019).</li><li>Hangx, S. J. T., Spiers, C. 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Eijlelkamp Soil &amp; Water Available from: <a target="_blank" href="https://www.eijkelkamp.com/download.php?file=M0853e_Calcimeter_b21b.pdf">https://www.eijkelkamp.com/download.php?file=M0853e_Calcimeter_b21b.pdf</a> (2020)</li><li>ASTM. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ASTM+D4373+-+Standard+test+method+for+rapid+determination+of+carbonate+content+of+soils.">ASTM D4373 - Standard test method for rapid determination of carbonate content of soils.</a> American Society of Testing of Materials. , (2014).</li><li>Sch&#246;nenberger, J., Momose, T., Wagner, B., Leong, W. H., Tarnawski, V. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Canadian+field+soils+I.+Mineral+composition+by+XRD/XRF+measurements.">Canadian field soils I. Mineral composition by XRD/XRF measurements.</a> International Journal of Thermophysics. 33 (2), 342-362 (2012).</li><li>Versteegh, E. A. A., Black, S., Hodson, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carbon+isotope+fractionation+between+amorphous+calcium+carbonate+and+calcite+in+earthworm-produced+calcium+carbonate.">Carbon isotope fractionation between amorphous calcium carbonate and calcite in earthworm-produced calcium carbonate.</a> Applied Geochemistry. 78, 351-356 (2017).</li><li>Soil Sampling. LSADPROC-300-R4. EPA Available from: <a target="_blank" href="https://www.epa.gov/sites/production/files/2015-06/documents/Soil-Sampling.pdf">https://www.epa.gov/sites/production/files/2015-06/documents/Soil-Sampling.pdf</a> (2020)</li><li>Smith, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+measure,+report+and+verify+soil+carbon+change+to+realize+the+potential+of+soil+carbon+sequestration+for+atmospheric+greenhouse+gas+removal.">How to measure, report and verify soil carbon change to realize the potential of soil carbon sequestration for atmospheric greenhouse gas removal.</a> Global Change Biology. 26 (1), 219-241 (2020).</li><li>. Measuring soil carbon change: A flexible, practical, local method Available from: <a target="_blank" href="https://soilcarboncoalition.org/measuring-soil-carbon-change-flexible-practical-local-method/">https://soilcarboncoalition.org/measuring-soil-carbon-change-flexible-practical-local-method/</a> (2021)</li><li>Haque, F., Santos, R. M., Chiang, Y. 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The authors have no conflict of interest.

Given that collecting samples from fertilized agricultural fields is usually difficult, it is suggested that samples should be collected before nutrient application. It is also advisable to avoid collecting samples from frozen fields. The sampling depth may vary in different areas depending on the ease of sampling over the vertical profile, and the depth of the water table. The selected soil sampling device is dependent on the soil structure and depth of interest33. While it is more convenient to ...

CO2 is a major greenhouse gas (GHG), and its concentration in the atmosphere is increasing continuously. Preindustrial global average CO2 was about 315 parts per million (ppm), and as of April 2020, the atmospheric CO2 concentration increased to over 416 ppm, hence causing global warming1. Therefore, it is critical to reduce the concentration of this heat-trapping GHG in the atmosphere. Socolow2 has suggested that to stabilize the concentration of atmospheric CO2 to 500 ppm by 2070, nine &#39;stabilization wedges&#39; will be required, where each stabilization wedge is an individual mitigation approach, sized to achieve 3.67 Gt CO2 eq per year in emissions reduction.
Carbon capture and storage (CCS) is the main technology to reduce the CO2 from the atmosphere, as recommended by the Mission Innovation initiative, launched at the United Nations Climate Change Conference 20153. To capture atmospheric CO2, the three main storage options available are ocean storage, geological storage, and mineral carbonation4. Focusing on mineral carbonation, CO2 is stored by converting alkaline earth metals, mainly calcium- and magnesium-rich silicates, into thermodynamically stable carbonates for geological timeframes (over millions of years)5. For example, olivine, pyroxene, and serpentine group minerals have the potential to undergo mineral carbonation6; however, under normal conditions, these reactions are limited by slow reaction kinetics. Therefore, to speed up the process under ambient conditions, finely comminuted (crushed/milled) forms of these silicates can be applied to agricultural soils, a process referred to as terrestrial enhanced weathering7. Soil is a natural sink to store CO2, presently being a reservoir for 2500 Gt of carbon, which is thrice the atmospheric reservoir (800 Gt carbon)8. Pedogenic processes in soils and subsoils regulate atmospheric CO2 by two major natural pathways, namely the organic matter cycle and the weathering of alkaline earth metal minerals, affecting organic and inorganic carbon pools, respectively9.
It is estimated that almost 1.1 Gt of atmospheric CO2 is mineralized through chemical rock weathering annually10. Silicate rocks rich in calcium and magnesium (e.g., basalt) are regarded as the primary feedstocks for enhanced weathering9,11,12. Once crushed silicate-containing minerals are applied to agricultural fields, they begin to react with CO2 dissolved in soil porewater, concluding with the mineral precipitation of stable carbonates11,13. Olivine14,15, wollastonite (CaSiO3)13, dolerite, and basalt16 are among minerals which have demonstrated carbon sequestration potential through enhanced weathering in previous studies. Despite the greater availability, and hence possibly greater CO2 sequestration capacity, of magnesium silicates, there are concerns about their application for enhanced weathering in croplands due to their potential environmental impact as a result of Cr and Ni leaching and the possible presence of asbestiform particulates11,15,17,18. As a calcium-bearing silicate, wollastonite is herein highlighted as a prime candidate for this process due to its high reactivity, simple chemical structure, being environmentally benign as well as facilitating the production of carbonates due to the weaker bonding of Ca ions to its silica matrix12,19,20,21. Wollastonite that is mined in Kingston, Ontario, Canada, and is presently commercialized by Canadian Wollastonite for agricultural applications, does not contain elevated levels of hazardous metals. The worldwide wollastonite reserves are estimated to be over 100 Mt, with China, India, USA, Mexico, Canada, and Finland as the top productive countries22.
Enhanced weathering of silicate mineral is reckoned to promote soil health, notably crop yield increase and plant growth improvement, leading to the potential reduction in the application of synthetic fertilizers, which can further contribute to GHG emissions reduction11,18,19. Previous studies have reported that the application of Ca-rich silicate minerals to soils supplies basicity for neutralizing acidity in the soil medium, favoring crop production23,24,25. This also impedes toxic metals mobilization, susceptible to acidic conditions, and enhanced weathering could be useful for retarding erosion through soil organic matter increment11.
Equations 1-3 show how pedogenic carbon sequestration as inorganic carbonates is possible by amending soils with wollastonite. Ambient CO2 enters the soil through rainwater or is produced in soil by microbial activity degrading organic compounds. Once in contact with soil porewater, carbonic acid is formed, which dissociates to form bicarbonate and proton (Equation 1). In the presence of plants, root exudates, such as citric acid and maleic acid, are released, which also provide protons in the system. These protons facilitate the dissolution of wollastonite in the soil through releasing Ca ions and leaving behind amorphous silica (Equation 2). The released Ca ions ultimately react with the bicarbonate to precipitate as carbonates (crystalline calcite or other varieties, depending on geochemical conditions) (Equation 3). This formed calcium carbonate becomes part of the soil inorganic carbon (SIC) fraction26.
Ambient CO2 solvation:
2CO2(g) + 2H2O(l) &#8596; 2H2CO3(aq) &#8596; 2HCO3- + 2H+ (1)
Wollastonite dissolution (H+ from the dissociation of carbonic acid and root exudates):
CaSiO3(s) + 2 H+ &#8594; Ca2+ + H2O(l) + SiO2(s)&#160;(2)
Pedogenic inorganic carbonate precipitation:
Ca2+ + 2 HCO3- &#8594;&#160; CaCO3(s)&#8595; + H2O(l) + CO2(g)&#160;(3)
In our recent work, enhanced weathering through the application of wollastonite to agricultural soils, as a limestone-alternative amendment, has been found effective for CaCO3 precipitation in topsoil, both at laboratory and field scales, and over short (few months) and long (3 years) terms. In the field studies, chemical and mineralogical assessments have revealed that the SIC content increases proportionally to wollastonite application dosage (tonne&#183;hectare-1)13. In laboratory studies, the mineralogical analysis showed the presence of pedogenic carbonate due to carbon sequestration19. Pedogenic carbonate formation in soil depends on several factors, most notably: topography, climate, surface vegetation, soil biotic processes, and soil physicochemical properties27. Our previous study23 determined the role of plants (a leguminous plant (green bean) and a non-leguminous plant (corn)) on wollastonite weathering and inorganic carbonate formation in soil. Our ongoing research on the pedogenic carbon formation and migration in soils and subsoils includes investigating the fate of soil carbonates in agricultural soil, first formed in topsoils due to mineral weathering at various depths and over time. According to Zamanian et al.27, the naturally occurring pedogenic carbonate horizon is found farther from the surface as the rate of local precipitation increases, with the top of this horizon commonly appearing between a few centimeters to 300 cm below the surface. Other ambient and soil parameters, such as soil water balance, seasonal dynamics, the initial carbonate content in parent material, soil physical properties, also impact the depth of this occurrence27. Thus it is of significance to sample soils to a sufficient depth at all opportunities to obtain an accurate understanding of the original and the incremental levels of SIC resulting from enhanced weathering of silicates.
At the field scale, an important limitation is the use of low application rates of silicate soil amendments. As there is limited knowledge on the effect of many silicates (such as wollastonite and olivine) on soil and plant health, commercial producers avoid testing higher application rates that could result in significant carbon sequestration. As a result of such low application rates, as well as the large area of crop fields, a research challenge commonly faced is to determine changes in SIC when values are relatively low, and to recover and isolate the silicate grains and weathering products from the soil to study morphological and mineralogical changes. In our past work, we reported on how physical fractionation of the wollastonite-amended soil (using sieving) enabled a better understanding of the weathering process, especially the formation and accumulation of pedogenic carbonates28. Accordingly, the higher contents of wollastonite and weathering products were detected in the finer fraction of soil, which provided reasonably high values during analyses, ensuring more precise and reliable results. The findings highlight the importance of using physical fractionation, through sieving or other segregation means, for reliable estimation of the sequestrated carbon accumulation in silicate-amended soils. However, the degree of fractionation could vary from soil to soil and from silicate to silicate, so it should be further researched.
Accurate measurement of SIC is critical for establishing a standard and scientific procedure that can be adopted by various researchers interested in analyzing the evolution of SIC and (and organic carbon) over time and depth of the soil. Such methodology enables farmers to claim carbon credit as a result of SIC formation in their field soils. The following protocol describes, in detail: (1) a soil sampling method to be used following soil silicate amendment, which accounts for the statistical significance of the analyzed soil data; (2) a soil fractionation method that improves the accuracy of quantifying changes in pedogenic inorganic carbonate pool as a result of enhanced silicate weathering, and (3) the calculation steps used to determine the SIC sequestration rate as a result of soil silicate amendment. For the purpose of this demonstration, wollastonite, sourced from Canadian Wollastonite, is assumed to be the silicate mineral applied to agricultural soils, and the agricultural soils are considered to be similar to those found in Southern Ontario&#39;s farmlands.
The procedure involving amending agricultural soil with wollastonite (e.g., determining the amount of wollastonite to apply per hectare, and the method to spread it over the soil) was described in our previous study13. The study area in our prior and present work is rectangular plots; therefore, the direct random sampling method is appropriate for such studies. This is a commonly used method owing to its low cost, reduced time requirement, and ability to provide adequate statistical uncertainty. Similarly, depending on the various field conditions and the level of statistical significance desired, zonal or grid sampling methods can also be used. Accuracy in soil sampling is essential to reduce statistical uncertainty as a result of sampling bias. When statistics are used, achieving less than 95% confidence (i.e., p &#60; 0.05) is not considered &#34;statistically significant.&#34; However, for certain soil studies, the confidence level may be relaxed to 90% (i.e., p &#60; 0.10) owing to the number of uncontrolled (i.e., naturally varying) parameters in the field conditions that affect the general precision of measurements. In this protocol, two sets of samples are collected in order to investigate SIC content and other chemical, mineral, and morphological properties of the soil throughout its vertical profile.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Analytical scale</td>
			<td>Sartorius</td>
			<td>Quintix 224-S1</td>
			<td>Four decimals.</td>
		</tr>
		<tr>
			<td>Calcimeter</td>
			<td>Eijkelkamp</td>
			<td>Model 08.53</td>
			<td>To determine the wt% CaCO3-equivalent in the sample.</td>
		</tr>
		<tr>
			<td>Drying cabinet/muffle furnace</td>
			<td>Thermo Scientific</td>
			<td>F48055-60</td>
			<td>50&#176;C or 103 &#177; 2&#176;C.</td>
		</tr>
		<tr>
			<td>HCl</td>
			<td>Fisher Scientific</td>
			<td>A144S-500</td>
			<td>Reagent grade (36.5%-38.0%).</td>
		</tr>
		<tr>
			<td>HNO3</td>
			<td>Fisher Scientific</td>
			<td>T003090500</td>
			<td>Trace metal analysis grade (69.0%-70.0%)</td>
		</tr>
		<tr>
			<td>Inductively Coupled Plasma Mass Spectrometer (ICP-MS)</td>
			<td>PerkinElmer</td>
			<td>NexION</td>
			<td>To determine the concentration of Ca in the microwave-digested soil.</td>
		</tr>
		<tr>
			<td>Microwave digester</td>
			<td>PerkinElmer</td>
			<td>Titan</td>
			<td>To digest soils in concentrated HNO3.</td>
		</tr>
		<tr>
			<td>pH meter</td>
			<td>Oakton</td>
			<td>700</td>
			<td>Calibrated with standard solutions before each set of measurements; temperature corrected to 25 &#176;C.</td>
		</tr>
		<tr>
			<td>Scanning Electron Microscope -Energy Dispersive Spectroscope (SEM-EDS)</td>
			<td>Oxford</td>
			<td>X-Max20 SSD</td>
			<td>To determine the morphology of soil particulates.</td>
		</tr>
		<tr>
			<td>Sieve shaker</td>
			<td>Retsch</td>
			<td>AS-200</td>
			<td>For soil fractionation.</td>
		</tr>
		<tr>
			<td>Soil auger sampler</td>
			<td>Eijkelkamp</td>
			<td>01-16</td>
			<td>Depths down to 700 cm.</td>
		</tr>
		<tr>
			<td>Soil Dakota probe sampler</td>
			<td>JMC</td>
			<td>PN139</td>
			<td>Depths down to 100 cm.</td>
		</tr>
		<tr>
			<td>Soil probe sampler</td>
			<td>JMC</td>
			<td>PN031</td>
			<td>Depths down to 30 cm.</td>
		</tr>
		<tr>
			<td>Soil moisture meter</td>
			<td>Extech</td>
			<td>MO750</td>
			<td>Measure moisture content up to 50%</td>
		</tr>
		<tr>
			<td>Wavelength Dispersive X-ray Fluorescence spectroscope (WDXRF)</td>
			<td>Malvern Panalytical</td>
			<td>Zetium</td>
			<td>To characterize elemental composition of soil.</td>
		</tr>
		<tr>
			<td>X-ray Diffraction analyzer (XRD)</td>
			<td>Panalytical</td>
			<td>Empyrean</td>
			<td>To characterize mineralogicalbproperties of soil.</td>
		</tr>
	</tbody>
</table>

monitoring pedogenic inorganic carbon accumulation due to weathering of amended silicate minerals in agricultural soils.

The present study aims to demonstrate a systematic procedure for monitoring inorganic carbon induced by enhanced weathering of comminuted rocks in agricultural soils. To this end, the core soil samples taken at different depth (including 0-15 cm, 15-30 cm, and 30-60 cm profiles) are collected from an agriculture field, the topsoil of which has already been enriched with an alkaline earth metal silicate containing mineral (such as wollastonite). After transporting to the laboratory, the soil samples are air-dried and sieved. Then, the inorganic carbon content of the samples is determined by a volumetric method called calcimetry. The representative results presented herein showed five folded increments of inorganic carbon content in the soils amended with the Ca-silicate compared to control soils. This compositional change was accompanied by more than 1 unit of pH increase in the amended soils, implying high dissolution of the silicate. Mineralogical and morphological analyses, as well as elemental composition, further corroborate the increase in the inorganic carbon content of silicate-amended soils. The sampling and analysis methods presented in this study can be adopted by researchers and professionals looking to trace pedogenic inorganic carbon changes in soils and subsoils, including those amended with other suitable silicate rocks such as basalt and olivine. These methods can also be exploited as tools for verifying soil inorganic carbon sequestration by private and governmental entities to certify and award carbon credits.

The SIC content of soils can be determined using various methods, including an automated carbon analyzer or a calcimeter. The automated carbon analyzer for total soil carbon determination measures the CO2 pressure built-up in a closed vessel30. In calcimetry, the evolved volume of CO2 released after acidification, typically by the addition of concentrated HCl acid, of the carbonate-containing sample is measured. The calcimetry method is relati...

Watch this Scientific Journal Video about Monitoring Pedogenic Inorganic Carbon Accumulation Due to Weathering of Amended Silicate Minerals in Agricultural Soils. at JoVE.com

Monitoring Pedogenic Inorganic Carbon Accumulation Due to Weathering of Amended Silicate Minerals in Agricultural Soils.

The verification method described here is adaptable for monitoring pedogenic inorganic carbon sequestration in various agricultural soils amended with alkaline earth metal silicate-containing rocks, such as wollastonite, basalt, and olivine. This type of validation is essential for carbon credit programs, which can benefit farmers that sequester carbon in their fields.

The present study aims to demonstrate a systematic procedure for monitoring inorganic carbon induced by enhanced weathering of comminuted rocks in ...

The verification method described here is adaptable for monitoring pedogenic, inorganic carbon sequestration in various agricultural soils amended with rocks containing alkaline earth metal silicates such as Wollastonite, basalt, and olivine. This method can be readily exploited by private or governmental entities for verifying soil inorganic carbon content in view of qualifying farmers for negative emission carbon credit. Enhanced weathering of minerals spread onto lands can also lead to carbon sequestration in scenarios beyond agriculture, such as pasture, forestry, or rehabilitated lands, and adrian soils.The heterogeneity of agriculture soils, both adrial and depth-wise, makes it challenging to determine inorganic carbon content accurately, and subsampling of samples also contributes to reduced precision. The use of standard additions of calcium carbonate sample dividers, extensive analysis replication, and statistical analysis can help first-time researchers gain confidence with the proposed methodology. Demonstrating part of the field procedures will be Stephen Vanderburgt, a master's student from our laboratory.Begin by determining leveling of each plot using a GPS receiver, then place flags at the boundaries of each plot to ease subsequent sampling. Collect core samples from random points within each subplot, one per subplot. Use a soil probe or a soil core sampler to collect the soil core down to three depth zones of zero to 15 centimeters, 15 to 30 centimeters, and 30 to 60 centimeters.Use an extendible auger to collect deep soil samples from additional locations down to three depth zones of 60 to 100 centimeters, 100 to 175 centimeters, and 175 to 250 centimeters. Transfer the soil samples into buckets, one per each sample depth at each plot. Hand blend the soils in each bucket thoroughly, then place the portable moisture tester into the mixed soil sample and wait until the moisture content fixes at a stable point on the gauge of the device.Press the holder button and record the value as the realtime moisture content of blended soils. Label sample bags properly with information about the plots, the soil depth, and date of sampling, then store the composite samples in the bags. Air dry the soil samples as soon as possible after sampling to minimize the oxidation of soil carbon.Place the soil samples in cardboard boxes and place the boxes in a drying cabinet at 50 degrees Celsius for 24 to 48 hours, until the soil is dry. Store the air dried samples in sample bags until further analysis. Prior to soil fractionation, run the soil samples through a two millimeter sieve to remove large fragments of rocks and plant remains.Oven dry the sieved soils by placing them in a muffle furnace maintained at 105 degrees Celsius, for at least 15 hours. For soil fractionation, place one kilogram of the oven dried sample onto the top mesh of the sieve shaker consisting of different mesh sizes. Shake the sieves at 60 RPM for 15 minutes.Use pan fractions of less than 50 micrometers for analyses, as this is the pedogenic carbonate enriched soil fraction. To determine the inorganic carbon content of soil samples using calcimetry analysis, place five grams of a sieved soil sample in an appropriate Erlenmeyer flask. Suspend the sample in 20 milliliters of ultra pure water.Add seven milliliters of four molar hydrochloric acid to a small flat bottomed glass test tube, then place this tube upright inside the flask using a pair of tweezers. Carefully attach the flask to the calcimeter by fixing the rubber stopper. Adjust and read the initial water level in the burette and seal its head space by turning the top valve to the measuring position.Shake the flask, thereby knocking over the acid tube, until the water level in the burette reaches a constant value and no bubbling is observed in the solution. A typical set of data for a Wollastonite amended soil compared to a control untreated soil is shown here. The pH of the amended soil is higher by 1.15 units compared to the control, and the calcium carbonate content is nearly five times greater.In the zero to 15 centimeter depth zone, the content was four times higher in the amended soil versus the control, and its pan fraction was enriched in calcium carbonate. The two deep profile samples had the highest contents, as these are naturally present carbonates in the C horizon. The various oxides present in the soil were determined by WDXRF.The main oxides present are those that make up the main soil minerals, plant nutrients, and the alkaline earth metals. The XRD pattern of a Wollastonite amended soil is shown here. The main peaks present are quartz and albite, which are predominant minerals in sandy, loamy soils.Peaks of the amended residual Wollastonite and of pedogenic calcite are also visible. Wollastonite amended soil was imaged using SEM after several weeks of weathering. A closer look at the Wollastonite particles shows the morphological changes occurring at the surface.Microanalysis of the Wollastonite surface was performed by obtaining an elemental mapping of the sample. The EDS spectrum of the mapped area revealed its semi-quantitative chemical profile. The earlier elemental maps clearly show that the detected silicon and calcium are largely found in the acicular Wollastonite particles.Spot EDS analysis was performed on the smaller fragments scattered in the soil sample. The fragments were rich in carbon and oxygen, suggesting that they are made up primarily of organic matter. When attempting this protocol, keep in mind that the sampling depth may vary in different areas, depending on the ease of sampling over the vertical profile, the thickness of the surface soil horizon, the depth of the water table, and soil structure.Measuring stable isotopic and radiogenic carbon signatures over the profile of soil and subsoil could be incorporated in this procedure to further verify the sequestration of atmospheric CO2 in mineral amended fields.

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4.9K Views.  University of Guelph. The verification method described here is adaptable for monitoring pedogenic, inorganic carbon sequestration in various agricultural soils amended with rocks containing alkaline earth metal silicates such as Wollastonite, basalt, and olivine. This method can be readily exploited by private or governmental entities for verifying soil inorganic carbon content in view of qualifying farmers for negative emission carbon credit. Enhanced weathering of minerals spread onto lands can also lead to car...